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Overview of Birth Defects

What is a birth defect?

A "birth defect" is a health problem or physical change, which is present in a baby at the time he/she is born. Birth defects may be very mild, where the baby looks and acts like any other baby, or birth defects may be very severe, where you can immediately tell there is a health problem present. Some of the severe birth defects can be life threatening, where a baby may only live a few months, or may die at a young age (in their teens, for example).

Birth defects are also called "congenital anomalies" or "congenital abnormalities." The word "congenital" means "present at birth." The words "anomalies" and "abnormalities" mean that there is a problem present in a baby.

What causes birth defects to occur?

There are many reasons why birth defects happen. Most occur due to environmental and genetic factors. About 40 percent of all birth defects have a known cause. The remaining 60 percent of birth defects do not have a known cause. You may find it surprising that scientists and physicians have not determined the cause for all birth defects. This is why there is a lot of research into the causes of birth defects, to understand more about why they happen and how to prevent them.

Who is affected by birth defects?

Birth defects have been present in babies from all over the world, in families of all nationalities and backgrounds. Anytime a couple becomes pregnant, there is a chance that their baby will have a birth defect. Most babies are born healthy. In fact, 97 out of 100 babies are born healthy. Anytime a couple becomes pregnant, there is a 3 to 4 percent chance that their baby will have a birth defect. The 3 to 4 percent number is sometimes called the background rate for birth defects, or the population risk for birth defects. In a family where birth defects are already present in family members or the parents themselves, the chance for a couple to have a child with a birth defect may be higher than the background rate of 3 to 4 percent.

What are the genetic and environmental causes of birth defects?

When a baby is born with a birth defect, the first question usually asked by the parents is "how did this happen?" Sometimes, this question cannot be answered. This can be very upsetting for parents because it is normal to search for and desire an answer as to why your baby has a health problem. For about 40 percent of birth defects, however, there is a known cause, which has to do with either genetic or environmental factors, or a combination of the two. Here is some general information and terms related to the different causes of birth defects:

Causes of Birth Defects Frequencies
Single Gene Defects 7.5 percent
Chromosome Abnormalities 6.0 percent
Multifactorial Inheritance 20.0 percent
Teratogens 4 to 5 percent
Unknown 60 percent

Why are birth defects a concern?

Although some birth defects have a single abnormality, others have abnormalities in multiple body systems or organs. Birth defects may cause life-long disability and illness, and with some, survival is not possible.

Some birth defects, such as mental retardation, are non-treatable disabilities. However, many physical defects can be treated with surgery. Repair is possible with many defects including cleft lip or palate, and certain heart defects.

How are birth defects diagnosed?

Many birth defects can be diagnosed before birth with special tests (prenatal diagnosis). Chromosomal abnormalities such as Down syndrome can be diagnosed before birth by analyzing cells in the amniotic fluid or from the placenta. Fetal ultrasound during pregnancy can also give information about the possibility of certain birth defects, but ultrasound is not 100 percent accurate, since some babies with birth defects may look the same on ultrasound as those without problems. A chromosome analysis, whether performed on a blood sample or cells from the amniotic fluid or placenta, is over 99.9 percent accurate.

Tests that help screen for birth defects include the following:

Sometimes, birth defects are not diagnosed until physical examination of the baby after birth. To confirm the physical findings, a small blood sample can be taken and the chromosomes can be analyzed. This information is important in determining the risk for that birth defect in future pregnancies.

Prevention of birth defects:

Research is ongoing to find and treat the causes of many birth defects. Immunizations of the mother against certain infections, such as rubella, can prevent infection. Much has been learned about the dangerous effects of alcohol on the developing baby and women are now advised to not drink during pregnancy. In recent years, a strong link has been discovered between the lack of the B-vitamin folic acid and the development of neural tube defects such as spina bifida. Taking a vitamin containing sufficient folic acid before conception and in early pregnancy can often help prevent many serious defects.

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Online Resources of Medical Genetics


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